Mechanical-electrical analog converter



1957 w. A. HANNIG ETAL 2,7

MECHANICAL-ELECTRICAL ANALOG CONVERTER Filed Oct. 13, 1953 Inventors: 1Wi||iamA.Hanni Arnoldl-ifiilver",

by v ll7/saz TheirAttoPney.

Sttes MECHANICAL-ELECTRICAL ANALGG CONVERTER William A. Hannig,chenectady, and Arnold H. Silver, Troy, N. Y., assignors to GeneralElectric Company, a corporation of New York Application October 13,1953, Seriai No. 385,812

tllaiins. (Cl. 323-79) This invention pertains to voltage dividingdevices, and more particularly to a mechanical-electrical analogconverter of the type used to convert a mechanical quantity into anelectrical quantity, and, in some applications, to perform amathematical operation on the electrical quantity obtained from theconversion.

Computing machines of the analog type, which operate on measurablephysical quantities rather than on numbers, are well-known in the art.When a problem which is expressed in numbers is to be solved by ananalog machine, the numbers are translated into physical form, such aslight intensities, electric voltages, lengths, or angular positions ofshafts, and the computing operations are performed on these physicalquantities.

In some applications it is desirable to convert a mechanical quantity,such as the angular position of a shaft, into an electrical quantity onwhich specific operations may be performed more easily than on amechanical quantity. A known method of making such a conversion is toconnect the shaft, Whose angular position is variable, to the rotatingarm of a rheostat or potentiometer, and thus establish a value ofcurrent or voltage which is controlled by the angular position of theshaft. The present invention is directed toward this type ofmechanical-electrical converter.

In many instances, the electrical quantity, whose value is determined bythe angular position of a rotatable shaft, must be controlled with greatprecision, and this requires that the rheostat or potentiometer which isconnected to the incoming data driving shaft be extremely accurate. Itis difiicult, as well as costly, to obtain a potentiometer which isphysically suitable for use in an analog converter and which has betterthan 0.1% accuracy, that is, in which the resistance of the windingdeparts from its proper value at any point by less than 0.1%.Accordingly, an object of the present invention is to provide aconverter of the type described, which utilizes conventionalpotentiometers of readily obtainable accuracy, wherein the possibleerror in the output voltage is substantially less than the possibleerror in previously known converters using such otentiometers.

Another object of the invention is to provide a mechanical-electricalanalog converter employing a plurality of potentiometers which may bearranged to minimize the possible error in any desired region or regionsof the output voltage range.

A further object is to provide an analog converter in which the ratio ofthe analog to the variable represented remains constant over the entirerange of operation.

A form of the invention which attains the foregoing objectives comprisesa fixed voltage divider for connection across a voltage source. Thevoltage divider includes a plurality of resistors connected in series,and across each of these resistors is connected a potentiometer, so thatonly a portion of the total input voltage appears across eachpotentiometer. The potentiometer shafts, whose angular positions controlthe positions of the potentiometer pick-off contacts, are mechanicallyconnected together so that when one shaft is rotated all of the shaftsrotate simultaneously. The input data driving shaft whose angularposition is to be converted to an electrical potential, is connected todrive one of the potentiometer shafts.

The relationships between the resistors of the voltage divider, theresistances of the otentiometers, and the gears which connect thepotentiometer shafts are such that each potentiometer covers a specificrange of output voltage corresponding to a specific range of rotation ofthe input data driving shaft, and means are provided to select theoutput from the various potentiometer pickotf contacts as the input datadriving shaft rotates through its various ranges. Thus, the output ofeach potentiometer is independent of any error of the otherpotentiometers.

Further features and advantages of the invention will become apparentfrom the following description taken in conjunction with theaccompanying drawing, which is a diagrammatic view of amechanical-electrical analog converter embodying the invention.

In the form of the invention illustrated, it is desired to convert themechanical rotation of an input data driving shaft 1 into an electricalpotential, whose value is determined by the angular position of thedriving shaft 1. A voltage source E1 (not shown), from which the outputvoltage is derived, may be connected across input terminals 2?; and 3,between which resistors 4, 5, 6, and 7 are connected in series to form avoltage divider. Resistors 4, 5, 6, and 7 may be either individual fixedresistors or sections of a large resistor having fixed or movable taps.In many instances, the latter arrangement is preferable in order thatall sections of the divider may respond the same way to temperaturevariations. Input terminal 2 may be grounded (as shown), or, as will belater pointed out, the ground connection may be omitted or placed atother points in the voltage divider.

An output voltage, which carries in accordance with the position of thedriving shaft 1, is taken from potentiometers 3, 9, l0, and 11, whoseends are electrically connected to the ends of resistors 4, 5, 6, and 7,respectively, with the resistance of each potentiometer being, ingeneral, equal to or greater than the resistor across which it isconnected. The ratio of the resistance of each potentiometer to theresistor across which it is connected need not be the same for allcombinations. However, if the resistors 4, 5, 6, and 7 all have the sametemperature vs. resistance characteristics, as when they are sections ofa single large resistor, it is desirable to select the potentiometers 8,9, 1d, and 11 so as to disturb the uniform characteristics as little aspossible. It has been found that when the resistance of eachpotentiometer is ten or more times the value of the resistor acrosswhich it is connected the slight diiferences in the temperature vs.resistance characteristics of the potentiometers cause only a negligiblechange in the characteristics of the parallel sections.

The potentiometers 8, 9, 10, and 11 have movable pickoff contact arms12, 13, 14, and 15, respectively, mounted on. shafts 16, 1'7, 18, and19, respectively. In this instance, each of the potentiometers is of thecontinuously rotatable type, in which the movable contact arm can passfrom one end of the resistance winding across a small gap to the otherend, and need not be rotated in a reverse direction to reach theopposite end of the winding. Also, in the form of the invention hereshown, the potentiometers are linearly Wound; that is, the resistance ofeach winding is uniformly distributed throughout its length.

The potentiometer shafts l6, 17, 12%, and w, are mechanically connectedtogether for simultaneous rotation, in this instance, by means of gears20, 21, 22, and 23, respectively, mounted on the shafts. The ratiobetween the gears associated with adiacent potentiometers is such thatthe ratio of the amounts of rotation of the shafts is the inverse of theratio of the parallel resistances of the resistors and potentiometers,or, to state it another way, the ratio of the amounts of rotation of theshafts is the inverse of the ratio of the voltage drops across theirotentiometers. For example, if resistors 4 and 5 had resistances of 1000ohms and 2000 ohms, respectively, and otentiometers 8 and 9 hadresistances of 10,000 ohms and 20,000 ohms, respectively, therebycausing twice the voltage drop across potentiometer 9 as acrosspotentiometer 8, gear 21 would be twice the circumference of gear 20, sothat for one revolution of the gear 20 the gear 21 would make one-halfrevolution. Similarly, if the resistors 5 and 6 have equal resistancesand if potentiometers 9 and 10 have equal resistances, the gear ratiobetween the gears 21 and 22 would 1:1; and if the resistors 6 and 7 haveresistances of 2000 ohms and 1000 ohms, respectively, and thepotentiometers 10 and 11have resistances of 20,000 ohms and 10,000 ohms,respectively, the ratio of gears 22 and 23 would be such that the shaft19 would make two revolutions for every revolution of the shaft 18. Thiscoordination between the parallel resistances of the resistors andotentiometers and the amounts of rotation of the potentiometer shaftsis-the basis for one of the outstanding advantages derived from ourinvention, because, when the potentiometers are linearly wound, as inthis embodiment, the voltages present on the pickotf contact arms allchange by the same amount for any given rotation of a potentiometershaft, although the absolute values of the various voltages aredifferent.

The input data driving shaft 1 is connected into the gear train by anyconvenient means, such as by being connected directly to the shaft 16 ofpotentiometer 8. If desired, the driving shaft might be connected to thegear train through a gear of the proper size mounted on the drivingshaft and meshing with any one of the gears of the train.

The rotatable pick-01f contacts 12, 13, 14, and of the potentiometersare electrically .connected to the con tacts of a selector switch 24,which is mechanically connected to the driving shaft '1 by conventionalmeans, such as a gear train 25, and the amount of rotation of thedriving shaft determines which one of the potentiometer pickoff contactswill be connected through the selector switch to its output terminal 26.The selector switch 24 may be of any conventional type, which may be somodified that the change from any input connection to "its adjacent onesmay be made smoothly and Without discontinuity. In the example shown,the connection between the selector switch and the input data drivingshaft would be such that .during the first revolution of the drivingshaft 1 the contact arm 12 of potentiometer 8 would be connected throughthe selector switch to the output terminal 26; during the second andthird revolutions of the driving shaft, potentiometer v9 would have itscontact arm 13 connected to the output terminal;

during the fourth and fifth revolutions the arm 14 of potentiometer 10would be so connected; and during the sixth revolution of the drivingshaft the contact arm 15 of potentiometer 11 would be connected throughthe switch to the output terminal..

In order to illustrate clearly the operation of this form of theinvention, specific values have been assigned to the various elements.These values have been arbitrarily chosen, with due regard to theteachings of the invention, as follows: resistor 4, 1000 ohms; resistor5, 2000 ohms; resistor 6, 2000 ohms; resistor 7, 1000 ohms;potentiometer 8, 10,000 ohms; potentiometer 9, 20,000 ohms;potentiometer 10, 20,000 ohms; potentiometer 11, 10,000 ohms. If thevoltage E1 applied between terminals 2 and 3 is taken to be 60 volts,and terminal 2 is .connected to ground as shown, the potentials atpoints 27, 28, 29, 30, and 31 will be 0 volts, 10, volts, 30 volts,volts, and volts, respectively.

The various potentiometer contact arms are illustrated in the positioncorresponding to zero rotation of the driving shaft 1. At this time,contact arm 12 of potentiometer 8 is connected through the selectorswitch to the output terminal 26 and, because there has been no rotationof the driving shaft, the output terminal is at zero potential. As thedriving shaft 1 rotates counterclockwise in response to incoming data,the contact arm 12- moves around the potentiometer in the samedirection, and the voltage appearing at the output terminal 26 increasesfrom zero volts to 10 volts as the driving shaft makes one completerevolution. After one revolution, the driving shaft causes the selectorswitch 24 to disconnect contact arm 12 from the output terminal andconnect contact arm 13 thereto. The potentiometer contact aims are soarranged with respect to each other that when the arm 12 ofpotentiometer 8 has made one revolution and is at the high potential endof the winding,

arm 13 of potentiometer 9 is at the low potential end of its winding.Thus, the arms 12 and 13 are at the same potential .and the transitionfrom one to the other may be made smoothly. Similar relationships existbetween all of the potentiometer contacts arms.

.As :the :incoming data driving shaft 1 continues to rotate through itssecond and third revolutions, the contact arm 13 of potentiometer 9rotates once around the winding of the potentiometer, and the voltageappearing at output terminal 26 rises from 10 volts to 30 volts. Thisaction results because, as previously stated, the ratio of theamounts-of rotation of the shafts of potentiometers 8 and 9 is theinverse of the ratio of the resistances of the parallel combination ofresistor 4 and potentiometer 8 'andthe parallel combination of resistor5 and potentiometer 9. That is, the parallel resistance of resistor 5and potentiometer 9 'is twice that of resistor 4 and potentiometer 8,and, therefore, the shaft 17 of potentiometer 9 rotateshalf as fast asthe shaft 16 of potentiometer 8. At the end of three revolutions of thedriving shaft 1 from its reference point, the potential on the contactarm 13 and output terminal 26 is 30 volts, and the driving shaft 1causes the selector switch to disconnect contact arm 13 from the outputterminal and connect contact arm 14 thereto.

The resistance ratio of the parallel combinations which includeresistors 5 and 6 andpotentiometers 9 and '10 is 1:1, and, therefore,the gears 21 and 22 are so selected that the shafts of potentiometers .9and 10 rotate at the same speed. At the end of three revolutions ofdriving shaft 1, contact arm 14 of potentiometer .10 is .at :thelowpotential end of .the winding and, during the next .two revolutions, .itwill rotate once around the potentiometer. During these two revolutionsthe potential vonoutput terminal .26 will rise from 30 to 5.0 volts.Upon completion of five revolutions of the driving shaft, the selectorswitch is caused to disconnect contact arm 14 and to connect contact arm15 to the output terminal.

Because the parallel combination ofresistor 6 and potentiometer-10 hastwice the resistance of the parallel combination of resistor 7 andpotentiometer 11, the gears 22 and 23 are so selected that the contactarm 15 of potentiometer 11 rotates twice as rapidly as contact .arm 14of potentiometer 10. Therefore, during the sixth revolution of "thedriving shaft 1, contact arm 15 of potentiometer :11 will rotate once,and the output voltage on terminal 26 will rise from 50 to :60volts.

Atthe .end .of six revolutions of the driving shaft, all of theotentiometers have again reached the positions shown, and contact arm 12of potentiometer 8is again connected through-the elector switch to theoutput terminal. It is apparent, therefore, that the illustratedembodiment of our invention'may be used only in'a system wherein therange .of input data is such that it rotates driving shaft 1 less thansix revolutions. It is to be understood, however, that any number ofresistors of various values may be employed in the fixed voltage dividerin association with a corresponding number of potentiometers. That is,although we have shown only a four section arrangement, any number ofsections may be used so long as the fundamental relationships betweenthe resistances of the sections and the gears connecting thepotentiometer shafts are maintained.

In this form of the invention, it is seen that the relationship betweenthe output voltage and the amount of rotation of the driving shaft froma reference point is a constant ratio. For example, if a singlerevolution of the driving shaft produces an output voltage change ofvolts, two revolutions of the driving shaft will produce an outputvoltage change of 20 volts. It is to be understood, however, that thisinvention is not limited to such a linear relationship, and this form ofthe invention is shown only for purposes of illustration anddescription.

By the use of our novel arrangement the error in the output voltage dueto the error in accuracy of any potentiometer can be greatly reducedover prior known systems. For example, the voltage drop between points27 and 31 is 60 volts, which is divided among four potentiometers with10 volts appearing across potentiometer 8, 20 volts across potentiometer9, 20 volts across potentiometer l0, and 10 volts across potentiometer11. If it is assumed that the acuracy of potentiometer 11, for example,is 0.1%, the possible error due to this potentiometer would then be .00110 or .01 volt. If the entire 60 volts were applied across a singlepotentiometer having 0.1% accuracy, the possible error could be .00l 60or .06 volt.

A further advantage of our invention is that the possible output errormay be minimized in any desired region or regions of the total rangerequiring high accuracy by employing a plurality of potentiometers inthese regions, that is, by covering the regions in small steps ratherthan in large steps. In the embodiment shown and described, the greatestaccuracy was desired at the beginning and end of the 60 volt, 6revolution range. Therefore, potentiometers and resistors of the propervalue to have only 10 volts voltage drop across them were employed inthese two regions. If additional accuracy were required in these twoareas, the combination of resistor 4 and potentiometer 8 might bereplaced by ten resistor-potentiometer combinations connected in series,with each combination having one-tenth the resistance of the combinationof resistor 4 and potentiometer 8. Similarly, such an arrangement mighthave been employed instead of the resistor 7 and the potentiometer 11.Therefore, assuming the voltages and potentiometer accuracies to be thesame as in the example given above, the maximum output error in therange covered by one of these potentiometers would be .001 volt insteadof .01 volt, as previously explained. Thus, we have provided an analogconverter having a great advantage over prior devices, and one which hassolved a troublesome problem in the computing machine field.

The embodiment of the invention which has been described herein isconstructed to produce an electrical output signal which is eitheralways positive or always negative, depending on how the voltage sourceis connected to the input terminals. It will be apparent that manydifferent arrangements may be used, however. For example, the groundconnection might be made to a point intermediate the ends of the voltagedivider, instead of to one of the input terminals, as shown. In thatcase, the output signal could be either positive or negative, dependingon the position of the input data driving shaft. In addition, the inputmay be from either an alternating current or direct current source, andthe operation as previously explained will remain unchanged.

This embodiment of the invention is suitable for use in convertingincoming data from mechanical shaft rotation to an electrical potential.However, there are many other uses for the device and the invention isnot to be limited to any particular application.

For example, the converter may be used as a multiplier of two variables.In the above description of operation, it was assumed that the voltageE1 applied between input terminals 2 and 3 was constant. Therefore, theoutput potential on terminal 26 was proportional only to the incomingdata driving shaft position. However, it is apparent that the voltageapplied between the input terminals, as well as the position of thedriving shaft 1, may be varied. In this instance, the output voltagewill-be proportional to both the voltage E1 and the position of thedriving shaft 1, and will be proportional to the product of these twovariables.

Similarly, the device may also be used as an arbitrary functiongenerator of one variable. The series of potentiometers may be woundnon-linearly to represent the function, each covering a portion of thefunction and being switched in and out by the driving shaft 1, aspreviously indicated. The driving shaft 1 would represent theindependent variable, and the output voltage would represent thearbitrary function of this variable varied in accordance with thevoltages appearing across the sections of the voltage divider and inaccordance with the non-linear windings of the potentiometers. If it isdesired to use linearly wound potentiometers, a similar result may beobtained by properly adjusting the voltage divider voltages to produce astraight-line approximation of an arbitrary function of the inputvariable.

It is apparent that we have provided a device which has manyapplications, and it is our intention not to be limited by the specificembodiment or application shown or described. Various changes andmodifications may be made by one skilled in the art without departingfrom the spirit of the invention, which is to be limited only by thescope of the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A precision mechanical-electrical analog converter, comprising avoltage divider for connection across a voltage source, said voltagedivider comprising a plurality of resistors connected in series, apotentiometer connected across each of said resistors, eachpotentiometer having a continuously rotatable pick-off contact armconnected to a rotatable shaft, means connecting the rotatable shafts ofthe potentiometers for simultaneous rotation, the means connecting therotatable shafts of the potentiometers comprising a motion translatingmeans interrelated to produce equal voltage changes on all of thepotentiometer pick-off contact arms for a given rotation of a shaft, aselector switch having a plurality of input terminals and an outputterminal, means electrically connecting said potentiometer pick-offcontact arms to the input terminals of said selector switch, and meansresponsive to rotation of the potentiometer shafts for operating saidselector switch.

2. A precision mechanical-electrical analog converter, comprising avoltage divider for connection across a voltage source, said voltagedivider comprising a plurality of resistors connected in series, apotentiometer connected across each of said resistors, eachpotentiometer having a continuously rotatable pick-ofi contact armconnected to a rotatable shaft, means for connecting the rotatable shaftof a potentiometer to a driving shaft for rotation therewith, a gearfixed to each rotatable potentiometer shaft, the gears fixed to adjacentpotentiometer shafts being meshed with each other and their ratio ofteeth being the same as the ratio of the voltage drops across theirrespective potentiometers, a selector switch, means electricallyconnecting said pick-ofl contact arms to said selector switch, and meansresponsive to the amount of rotation of said driving shaft from areference point to operate said selector switch.

3. A precision mechanical-electrical analog converter comprising atleast two potentiometers connected in series for connection acrossavolta-ge source, each potentiometer having a continuously movablepick-E contact arm, actuating means for said contact arms forsimultaneous movement thereof in response to movement of an input datashaft, said actuating means including a variable motion transmittingmeans coupled to said arms so that movement thereof is inverselyproportional to the ratio ofthe voltage drops across their associatedpotentiometers, and means-responsive tome-movement of said pickotfi armsfor successively selecting-the output voltage existing ateach of saidpick-off arms.

4. A precision mechanical-electrical analog converter comprising aplurality of potentiometers connected in series for connection acrossavoltage source, each potentiometer having a continuously rotatablepick-off contactarm, actuating meansforsaid contact arms forsimultaneous rotation thereof in response to rotation of an input datashaft, said actuating means including a rotatable shaft secured to eachof said contact arms and variable motion transmitting means coupled tosaid shafts so that the, rotationthereof is inversely proportional to'the ratio of the, voltage drops across their associated potentiometers,andselector means operable by'said input shaft for successivelyselecting the output voltage existing at each of said potentiometerspick-off contact arms.

5. A precision mechanical-electrical analog converter,

8 comprising ac voltage divider for'connection across a voltage source;said voltage divider comprising aplurality'ofi resistors connected inscri es; a potentiometer connected across each'of'said resistors, eachpotentiometer having-a continuously rotatable picleo'ifcontact arm;actuating means for said contact arms for simultaneous rotation thereofin* response to rotation of an input data shaft, said actuating meansincluding a rotatable shaft secured to each of said contact arms, andvariable motion transmitting means coupled to said shafts so that therotation" thereof is inversely proportionalto the ratio of the voltagedrop across their associated otentiometers, a selector switch having aplurality of input t'errninalsand an output'terrninal and meanselectrically connecting said p0 tentiometer pick-oft contact arms to theinput terminals of said selector switch, and means" responsive torotationof said input data shaft for operating said selector switch;

References-(iited in the file ofthis patent UNITED STATES PATENTS

